The present invention relates to a color-conversion light-emitting device having a long service life, a method of manufacturing, the color-convention light-emitting device, and a display using the device. More particularly, the present invention relates to a color-conversion light-emitting device used for a display of an image sensor, personal computer, word processor, television set, facsimile machine, audio equipment, video equipment, car navigator, electronic desktop calculator, phone, mobile terminal, industrial measuring instrument, and the like.
In recent years, the information technology has been rapidly advanced. A display device used in the information technology has been required to have a better aesthetic appearance, a lighter weight, a thinner thickness and higher performance. Furthermore, a great effort has been made to reduce power consumption and increase a response speed. In particular, many attempts have been made to develop a high-definition full-color display device.
As opposed to a liquid crystal display device, an organic electro-luminescence device (hereinafter referred to as ‘organic EL’) has been developed as a device having wide-angle visibility and faster response. As a display device, the organic EL display device has characteristics such as (1) high luminance and high contrast, (2) low driving voltage and high emission efficiency, (3) high resolution, (4) wide-angle visibility, (5) high response speed, (6) high definition and multi-color display, (7) lightweight and small thickness, and the like. Thus, the organic EL device is expected to have a better aesthetic appearance, a lighter weight, a thinner thickness and higher performance.
Tohoku Pioneer Corporation has already developed a product with a vehicle-mounted green monochrome organic EL display in November 1997. In order to meet the need of the society, it is desirable to develop an improved organic EL display that is stable for an extended period of time, responds quickly, and displays multiple colors or full colors with high definition.
As a method for manufacturing the organic EL display device for displaying a desired color, a method in which a fluorescent material converts light emitted from a light emitting element to obtain a desired color has been used for a CRT and a plasma display. For example, Japanese Patent Publications No. 03-152897, No. 05-258860, No. 08-286033, and No. 09-208944 have disclosed a color conversion method in which a filter is composed of a fluorescent material for absorbing light with a wavelength in a region of light emitted from an organic light emitting device, so that the fluorescent material emits fluorescence with a wavelength in a visible light region.
In this approach, it is possible to use an organic light emitting device emitting a color other than white, so that the organic light emitting device has higher brightness as a light source. In a case of the color conversion method using an organic light emitting device emitting blue light, a frequency of the blue light is converted to that of green or red light. A color conversion filter containing a fluorescent material with such color conversion effect may be formed in a high-resolution pattern. Accordingly, it is possible to provide a full-color light emitting display even with weak energy light such as near-ultraviolet light or visible light.
FIG. 1 is a view showing a conventional color-conversion light-emitting device. The light-emitting device is provided with a light-emitting unit (opaque electrode 1, organic EL layer 2, and transparent electrode 3), a color-conversion layer 4 for converting a wavelength distribution of light emitted from the light-emitting unit, and a color filter layer 5. The light-emitting unit emits blue light as luminescent light, and the color-conversion layer converts the blue light to red or green light.
The color-conversion layer 4 contains a so-called “color-conversion colorant”, and the colorant absorbs light 50 from the light-emitting unit and emits fluorescence 60 with a different wavelength through wavelength conversion. It is known that the color-conversion colorant in the color-conversion layer 4 gradually decomposes due to a decomposition reaction resulting from excitation over a long-term use, thereby lowering long-term stability of the color-conversion layer 4.
Among various methods for preventing such a problem in the long-term stability, there has been a method in which the color-conversion layer 4 is made thicker to effectively prevent the problem. However, in the case of a multicolor display formed of a number of color-conversion light-emitting elements, it is difficult to increase a thickness of the color-conversion layer 4 relative to a width of each of the color-conversion light-emitting elements (pixel width). In consideration of a manufacturing process and a viewing-angle, when a pixel width is 50 μm, the color conversion layer needs to have a thickness of no more than 20 μm, preferably 10 μm or less.
Further, it is necessary to increase a concentration of the color-conversion colorant in the color-conversion layer to a very high level, so that the color-conversion layer having such a small thickness has sufficiently large absorption. When the color-conversion layer contains an extremely high concentration of the color-conversion colorant, the color-conversion efficiency is reduced due to concentration quenching. Also, the color-conversion efficiency tends to deteriorate over time due to a higher probability of the decomposition reaction of the color-conversion colorant. As a result, in the current color-conversion system, it is necessary to optimize a balance among the long-term stability, color-conversion efficiency, and manufacturing process to improve the performance.
In view of the problems described above, the present invention has been made, and an object of the present invention is to provide a color-conversion light-emitting device with improved performance without compromising the long-term stability color-conversion efficiency, and manufacturing process.
Another object of the invention is to provide a method of manufacturing the color-convention light-emitting device, and a display using the device.
Further objects and advantages of the invention will be apparent from the following description of the invention.